The present invention relates generally to radio frequency transmission lines. More particularly, the present invention relates to very high frequency (VHF) sharp-tuned elliptic filters.
Traditional broadcast television (TV) guidelines forbade transmission on adjacent channels in VHF (channels 2 through 13) or UHF (channels 14 through 83) bands in a single service area. This prevented ordinary TV receivers, which previously had limited out-of-band signal rejection capability, from receiving multiple channels simultaneously. A service area is defined to include the realistic good-reception range for TV channels at the transmitter power levels allocated to them by the Federal Communications Commission (FCC). Thus Minneapolis and St. Paul, Min., would be placed in the same service area for frequency allocation purposes, while Philadelphia, Pa. and New York, N.Y. would not. With increasing demand for channel allocations, this rule is in the process of being eased, which will permit, to choose an arbitrary example, channels 8 and 9 to be used in the same service area.
While typical TV receivers have improved significantly regarding out-of-band signal rejection, the burden remains on TV transmitters to ensure that each transmitted channel is essentially free of out-of-band emissions. This in turn demands improved capability in the final filters inserted in the transmission lines between transmitters and antennas for all channels. Existing RF filters for transmission lines typically employ Chebyshev filter architecture, which is well-behaved in the pass band but achieves less than optimum rolloff rate while providing more stop band attenuation than is normally needed.
It is therefore a feature and advantage of the present invention to implement the elliptic filter model, which provides sharp rolloffxe2x80x94that is, rapid transition from in-band signal passing to out-of-band signal rejectionxe2x80x94in a high-performance, high-power transmission line filter.
It is another feature and advantage of the present invention to provide low insertion loss in a high-performance, high-power transmission line filter.
It is another feature and advantage of the present invention to optimize phase characteristics across the pass band in a high-performance, high-power transmission line filter.
The above and other features and advantages are achieved through the application of a novel folded signal path, and through the inclusion of suitable coupling apparatus, as herein disclosed.
In one aspect, the invention provides a sharp-tuned very high frequency (VHF) elliptic filter, comprising a conductive enclosure that defines a signal path compatible with propagation of radio frequency (RF) energy in some portion of the VHF frequency range; a VHF-compatible input penetration configured to allow RF energy arriving at the enclosure to pass within; a VHF-compatible input coupling device configured to allow the RF energy impressed at the input penetration to radiate inside the conductive enclosure; a plurality of RF resonators within the enclosure, each configured to absorb and reradiate the RF energy; a plurality of RF coupling adjusters within the enclosure, each configured to restrict propagation of RF energy from one resonator to the next; a conductive baffle within the enclosure, so positioned that a portion of the signal path exists on both sides of the baffle; an internal coupling mechanism, configured to transfer RF energy through the conductive baffle; a VHF-compatible output penetration configured to allow RF energy present within the enclosure to pass out; and a VHF-compatible output coupling device configured to allow the RF energy present within the conductive enclosure to couple to the output penetration.
In another aspect, the invention provides an apparatus for sharp-tuned filtering of very high frequency (VHF) radio frequency (RF) energy, comprising means for enclosing an RF signal propagation path in a manner compatible with a portion of the VHF frequency range; means for admitting and radiating VHF energy into the enclosed path; means for absorbing and reradiating the VHF energy through a plurality of resonating means; means for restricting propagation of the VHF energy through the resonating means by a plurality of coupling adjustment means; means for guiding the VHF energy within the RF signal propagation path by partitioning; means for coupling the VHF energy between the resonating means otherwise isolated by the partitioning; and means for passing the VHF energy out through the boundary of the enclosing means.
In yet another aspect, the invention provides a method of sharp-tuned filtering of VHF energy, comprising the following steps: enclosing an RF signal propagation path in a manner compatible with a portion of the VHF frequency range; admitting and radiating the VHF energy into the enclosed path; absorbing and reradiating the VHF energy through a succession of resonant elements; restricting propagation of the VHF energy between successive resonant elements by a plurality of coupling adjustments; guiding the VHF energy within the RF signal propagation path by establishment of internal partitioning; coupling the VHF energy between the resonant elements otherwise isolated by partitioning; and passing the VHF energy out through the boundary of the signal propagation path.
There have thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and that will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.